This invention relates to a picture processor which is used especially in industrial or medical X-ray television and which processes a digitized picture signal to improve a picture.
In industrial or medical X-ray television, a prior-art picture processor for reducing the statistical noise of a radiation picture has been as shown in FIG. 4. In the figure, numeral 10 designates a picture memory consisting of M.times.N picture elements or pixels, and numeral 30 designates an adder.
In the picture processor thus constructed, a digitized input picture signal I.sub.i (X.sub.m, Y.sub.n) at a time t.sub.i and the value C.sub.i-1 (X.sub.m, Y.sub.n) of the picture memory (two-dimensional memory) 10 at time t.sub.i-1 are added by the adder 30, whereupon the sum is sent to the picture memory 10 and becomes the value C.sub.i (X.sub.m, Y.sub.n) thereof at the time t.sub.i. (X.sub.m, Y.sub.n) indicates the position of the picture element. The above calculation is performed for the respective pixels in succession, and the adding operations for all of the M.times.N pixels and the updating operations of the picture memory 10 are executed during the period of time .DELTA.t=t.sub.i -t.sub.i-1. .DELTA.t is usually 60 ms which is the television rate. The content of the picture memory 10 is output as a processed picture signal.
Next, the operation of the prior-art picture processor will be described more in detail. The picture signal intrinsically includes quantum noise based on statistical properties in the course of the imaging process thereof. Therefore, when the signal intensity is low, the quantum noise is greatly influential and degrades the contrast, the resolution, etc. In case of a still picture, accordingly, a process is performed in which the picture signals are digitized and the digital data items are integrated for each pixel so as to reduce the influence of the quantum noise. In FIG. 4, the value C.sub.i (X.sub.m, Y.sub.n) of the picture memory 10 at the time t.sub.i is obviously the integration ##EQU1## of the picture signals I.sub.j (X.sub.m, Y.sub.n) input till then. Accordingly, in the processed picture which has been generated by reading out the content of the picture memory 10, the relative statistical error ascribable to the quantum noise is improved .sqroot.N times where N denotes the number of times of the adding operations.
The input and output signals of the picture processor corresponding to on line are respectively shown in FIGS. 5(a) and 5(b). The outpt signals become N times the input signals as to the respective pixels, and have their statistical errors improved .sqroot.N times. However, although the case of general shading characteristics is illustrated in the figures, the signal intensity on a picture differs depending upon places, so that even after the processing, the magnitudes of the statistical errors differ depending upon pixels and are not uniform in the entire frame. In the illustrated case, therefore, it can occur that the statistical error of a peripheral part is greater than the statistical error of a middle part, and that even when illustrated signals S.sub.1 and S.sub.2 superposed on the convex signal are equal in the intensity (contrast) relative to the convex signal, the middle signal S.sub.1 is discriminated, whereas the peripheral signal S.sub.2 is not discriminated. Even in a case where the statistical quantum noise in the surroundings is lowered owing to a satisfactory integration, so the signal S.sub.2 can also be discriminated, man is sometimes unable to simultaneously discern the signals S.sub.1 and S.sub.2 with the naked eye when the integrated picture is displayed on a monitor screen. This is attributed to the facts that the dynamic range of the visual system of man is narrow and that the difference of luminosities is too great between the bright part and dark part of the integrated picture.
Since the prior-art picture processor is constructed as described above, the effect of reducing the quantum noise of an integrated picture differs for each pixel, and even a signal having the same contrast can be discriminated or not, depending upon the intensity of a peripheral signal. Another disadvantage is that when the integrated picture is displayed on a monitor screen, the luminosity difference between the bright part and dark part of the picture is great, so even a signal discriminated from quantum noise cannot be discerned by the vision of man whose dynamic range is limited.